Physiological responses and RPE during underwater treadmill walking in women of middle and advanced age

The purpose of this study was to examine the physiological responses and RPE during water walking using the Flowmill, which has a treadmill at the base of a water flume, in order to obtain basic data for prescribing water walking for people of middle and advanced age. Twenty healthy female volunteers with an age of 59.1 +/- 5.2 years took part in this study. They belonged to the same swimming club and regularly swam and exercised in water. Walking in water took place in the Flowmill. Subjects completed four consecutive bouts of 4 min duration at progressively increasing speeds (20, 30, 40 and 50 m/min) with 1 min rest between each bout. In addition, water velocity was adjusted to the walking speed of each bout. Subjects were instructed to swing both arms in order to maintain their balance during walking in water. The water depth was to the level of the xiphoid process and the water temperature was 30.31 +/- 0.08 degrees C. Both heart rate (HR) and oxygen uptake (VO2) increased exponentially as walking speed increased. HR was 125 +/- 15 bpm, and VO2 was 18.10 +/- 2.72 ml/kg.min-1 during walking in water at 50 m/min, which was the highest speed. The exercise intensity at this speed was equivalent to 5.2 +/- 0.8 Mets. The relationship between HR and VO2 during walking in water showed a highly significant linear relationship in each subject. There was also a highly significant linear relationship in the mean HR and VO2 of all subjects. Blood lactate concentration (LA) measured at rest and immediately after each bout was 1.1 +/- 0.4 mmol/l at rest, 1.0 +/- 0.2 mmol/l at 20 m/min, 1.0 +/- 0.3 mmol/l at 30 m/min, 1.1 +/- 0.2 mmol/l at 40 m/min, and 2.4 +/- 0.7 mmol/l at 50 m/min. LA at 50 m/min was significantly higher than at rest and at the other speeds. The relationship between HR and RPE during walking in water showed a highly significant linear relationship. The relationship between walking speed and energy expenditure calculated from VO2 and the respiratory exchange ratio (R) showed a high significant exponential relationship. These results suggested that HR and RPE can be effective indices for exercise prescription during Flowmill walking as with land walking.